1. Field of the Invention
The present invention relates generally to methods for fabricating magnetic transducer structures. More particularly, the present invention relates to a pole trimming method for fabricating inductive magnetic write head structures.
2. Description of the Related Art
The recent and continuing advances in computer and information technology have been made possible not only by the correlating advances in the functionality, reliability and speed of semiconductor integrated circuits, but also by the correlating advances in the storage density and reliability of direct access storage devices (DASDs) employed in digitally encoded magnetic data storage and retrieval.
Storage density of direct access storage devices (DASDs) is typically measured as areal storage density of a magnetic data storage medium formed upon a rotating magnetic data storage disk within a direct access storage device (DASD) magnetic data storage enclosure. The areal storage density of the magnetic data storage medium is defined largely by the track width, the track spacing and the linear magnetic transition density within the magnetic data storage medium. The track width, the track spacing and the linear magnetic transition density within the magnetic data storage medium are in turn determined by several principal factors, including but not limited to: (1) the magnetic read-write characteristics of a magnetic read-write head employed in reading and writing digitally encoded magnetic data from and into the magnetic data storage medium; (2) the magnetic domain characteristics of the magnetic data storage medium; and (3) the separation distance of the magnetic read-write head from the magnetic data storage medium.
With regard to the magnetic read-write characteristics of a magnetic read-write head employed in reading and writing digitally encoded magnetic data from and into a magnetic data storage medium, it is known in the art of magnetic read-write head fabrication that increased track spacings of magnetic data tracks within magnetic data storage media are required when employing inductive magnetic write heads which exhibit increased write fringe fields bridging their magnetic transducer pole layers. Increased write fringe field widths within inductive magnetic write heads typically result from non-symmetric magnetic pole layers within those inductive magnetic write heads. A schematic cross-sectional diagram of a typical inductive magnetic write head formed with non-symmetric magnetic pole layers is illustrated in FIG. 1.
Shown in FIG. 1 is a substrate 10 having formed thereupon a lower magnetic pole layer 12 separated from an upper magnetic pole tip 16a within a patterned upper magnetic pole layer 16 by a gap filling dielectric layer 14. Also shown in FIG. 1 bridging from the lower magnetic pole layer 12 to the patterned upper magnetic pole layer 16 is a pair of write fringe fields 15a and 15b.
It is also known in the art of magnetic read-write head fabrication that write fringe fields, such as the write fringe fields 15a and 15b as illustrated in FIG. 1, formed incident to non-symmetric magnetic pole layer alignment within inductive magnetic write heads, may be significantly reduced by partially etching the wider of the two non-symmetric magnetic pole layers while employing the narrower of the two non-symmetric magnetic pole layers as a mask to form within the wider of the two non-symmetric magnetic pole layers a pole tip self-aligned with the pole tip within the narrower of the two non-symmetric magnetic pole layers. A schematic cross-sectional diagram illustrating the results of such partial etching practiced upon the lower magnetic pole layer 12 as illustrated in FIG. 1 is shown in FIG. 2.
Shown in FIG. 2 is a partially etched lower magnetic pole layer 12' having formed therein a lower magnetic pole tip 12a separated from the upper magnetic pole tip 16a within a partially etched patterned upper magnetic pole layer 16' by a patterned gap filling dielectric layer 14'. There is also shown in FIG. 2 bridging from the partially etched patterned upper magnetic pole layer 16' to the partially etched lower magnetic pole layer 12' a pair of significantly reduced write fringe fields 15a' and 15b'.
While the inductive magnetic write transducer structure as illustrated in FIG. 2 typically exhibits significantly reduced write fringe fields in comparison with the inductive magnetic write transducer structure as illustrated in FIG. 1, the inductive magnetic write transducer structure as illustrated in FIG. 2 is typically not formed entirely without difficulties. One of the difficulties typically encountered when forming the inductive magnetic write transducer structure as illustrated in FIG. 2 is that a substantial portion of the patterned upper magnetic pole layer 16' under circumstances where: (1) the lower magnetic pole layer 12 and the patterned upper magnetic pole layer 16 are both formed of a permalloy (ie: nickel-iron, 80:20 w/w) magnetic material, as is common in the art of magnetic read-write head fabrication, (2) the gap filling dielectric layer 14 is simultaneously formed of an aluminum oxide dielectric material, as is similarly common in the art of magnetic read-write head fabrication; and (3) the magnetic write transducer structure whose schematic cross-sectional diagram is illustrated in FIG. 2 is etched from the magnetic write transducer structure whose schematic cross-sectional diagram is illustrated in FIG. 1 through an ion beam etch (IBE) method employing argon ions, as is similarly also common in the art of magnetic read-write head fabrication. The substantial portion of the patterned upper magnetic pole layer 16 is typically eroded due to an ion beam etch (IBE) selectivity of the ion beam etch (IBE) method for the patterned upper magnetic pole layer 16 with respect to the gap filling dielectric layer 14. Typically, the ion beam etch selectivity of the patterned upper magnetic pole layer 16, when formed of a permalloy magnetic material, with respect to the gap filling dielectric layer 14, when formed of an aluminum oxide dielectric material, is from about 1:0.3 to about 1:0.6.
Erosion of upper magnetic pole layers, such as the patterned upper magnetic pole layer 16, has been noted in the art of inductive magnetic read-write head fabrication, and it is typical in the art of inductive magnetic read-write head fabrication to compensate for the erosion by forming an upper magnetic pole layer with a substantial additional thicknesses beyond the thickness ultimately desired for a partially etched upper magnetic pole layer formed from the upper magnetic pole layer. See, for example, Krounbi et al., U.S. Pat. No. 5,438,747 (col. 11, line 68 to col. 12, line 5). Unfortunately, patterned upper magnetic pole layers, such as the patterned upper magnetic pole layer 16, formed with substantial additional thicknesses and thus significant aspect ratios, are often difficult to reproducibility form within magnetic transducer structures.
Although not specifically illustrated in FIG. 2, when fabricating a merged inductive write-magnetoresistive (MR) read magnetic head from the magnetic transducer structure whose schematic cross-sectional diagram is illustrated in FIG. 2, the partially etched lower magnetic pole layer 12' also serves as a top shield layer for a magnetoresistive (MR) sensor layer formed beneath the partially etched lower magnetic pole layer 12' within the merged inductive write-magnetoresistive (MR) read magnetic head. Under such circumstances, it is important that the partially etched lower magnetic pole layer 12' have sufficient remaining thicknesses at locations other than the location of the lower magnetic pole tip 12a in order to serve adequately as a top shield layer within the merged inductive write-magnetoresistive (MR) read magnetic head. While it is theoretically possible to assure adequate thicknesses of various portions of the partially etched lower magnetic pole layer 12' by increasing the thickness of the lower magnetic pole layer 12 from which is formed the partially etched lower magnetic pole layer 12', unfortunately, the thickness to which the lower magnetic pole layer 12 may be formed is itself often limited by design considerations when fabricating an inductive write-magnetoresistive (MR) read magnetic head.
A related consideration pertinent to providing the partially etched lower magnetic pole layer 12' with sufficient thicknesses at locations other than the location of the lower magnetic pole tip 12a to serve adequately as a top shield layer for a magnetoresistive (MR) sensor layer fabricated beneath the partially etched lower magnetic pole layer 12' is that the etch rate of the partially etched lower magnetic pole layer 12' near the upper magnetic pole tip 16a within the partially etched patterned upper magnetic pole layer 16' is, as is illustrated in FIG. 2, reduced. The etch rate is reduced due to a shadowing effect inherent in the ion beam etch (IBE) method through which is conventionally formed the partially etched lower magnetic pole layer 12'. Due to the shadowing when the partially etched lower magnetic pole layer 12' is formed through the ion beam etch (IBE) method, there is formed as illustrated in FIG. 2 the lower magnetic pole tip 12a with a projection T.sub.2 with respect to immediately surrounding portions of the partially etched lower magnetic pole layer 12', while portions of the partially etched lower magnetic pole layer 12' further removed from the lower magnetic pole tip 12a are etched to remove a thickness T.sub.1 with respect to the lower magnetic pole layer 12, as illustrated in FIG. 2. In that regard, it is desirable within merged inductive write-magnetoresistive (MR) read magnetic head fabrication to provide partially etched lower magnetic pole layers, such as the partially etched lower magnetic pole layer 12', formed through etch methods which provide minimal shadowing, thus yielding partially etched lower magnetic pole layers where values of parameters which correspond with T.sub.1 and T.sub.2 are most closely approximate.
By way of example, if it is assumed that: (1) the etch rate of the material from which is formed the gap filling dielectric layer 14 as shown in FIG. 1 is equal to R.sub.gap ; (2) the etch rate of the material from which is formed the lower magnetic pole layer 12 as shown in FIG. 1 is equal to R.sub.ip ; (3) the gap thickness is equal to G as shown in FIG. 2; (4) the etch time is equal to t; and, (5) the convention ion beam etch (IBE) method shadowing effect provides an etch rate of the portion of the partially etched lower magnetic pole layer 12' most closely adjoining the partially etched patterned upper magnetic pole layer 16' one half the etch rate of the patterned lower magnetic pole layer 12' further removed from the partially etched patterned upper magnetic pole layer 16', as illustrated in FIG. 2, then the thicknesses T.sub.1 as illustrated in FIG. 2 is determined in accord with equation 1 and the thickness T.sub.2 as illustrated in FIG. 2 is determined in accord with equation 2. EQU T.sub.1 =(t-G/R.sub.gap)R.sub.ip ( 1) EQU T.sub.2 =(t-2G/R.sub.gap)R.sub.ip /2=nG (2)
Within equation 2, n typically varies from about 0.5 to about 3. Equation 3, equation 4 and equation 5 then follow from equation 1 and equation 2 EQU t=2nG/R.sub.ip +2G/R.sub.gap ( 3) EQU T.sub.1 =(2nG/R.sub.ip +G/R.sub.gap)R.sub.ip ( 4) EQU T.sub.1 /T.sub.2 =T.sub.1 /nG=2+R.sub.ip /nR.sub.gap ( 5)
Thus, it is seen from equation 5 that by selectively etching the material from which is formed the gap filling dielectric layer 14 with respect to the material from which is formed the lower magnetic inductor pole layer 12 within FIG. 1 there will be minimized the magnitude of T.sub.1 with respect to T.sub.2 as illustrated in FIG. 2.
A related difficulty encountered when forming from the patterned upper magnetic pole layer 16 whose schematic cross-sectional diagram is illustrated in FIG. 1 the partially etched patterned upper magnetic pole layer 16' whose schematic cross-sectional diagram is illustrated in FIG. 2 is illustrated by the schematic plan-view diagram of FIG. 3 and the schematic cross-sectional diagram of FIG. 4. The schematic plan-view diagram of FIG. 3 corresponds with the schematic cross-sectional diagram of FIG. 1. Shown in FIG. 3 is the gap filling dielectric layer 14 having formed thereupon the patterned upper magnetic pole layer 16, which in turn in part has formed thereupon a patterned photoresist layer 18 as is commonly employed to protect the coil region R2 of the patterned upper magnetic pole layer 16 when etching the pole tip region R1 of the patterned upper magnetic pole layer 16 to form the partially etched patterned upper magnetic pole layer 16'. Shown in FIG. 4 is a schematic cross-sectional diagram illustrating the results of etching the patterned upper magnetic pole layer 16 whose schematic plan-sectional diagram is illustrated in FIG. 3 to form the partially etched patterned upper magnetic pole layer 16'. The schematic cross-sectional diagram of FIG. 4 is obtained through the cross-sectional plan perpendicular to the cross-sectional plane employed in obtaining the schematic cross-sectional diagram of FIG. 2.
Shown in FIG. 4 is the partially etched lower magnetic pole layer 12' having formed thereupon the patterned gap filling dielectric layer 14' which in turn has formed thereupon or thereover: (1) a magnetic coil isolation dielectric layer 20 having formed therein a series of magnetic coils 22; (2) the partially etched patterned upper magnetic pole layer 16'; (3) and the patterned photoresist layer 18. As is illustrated in FIG. 4, the partially etched patterned upper magnetic pole layer 16' has a step 24 formed therein at the location of the patterned photoresist layer 18. The step 24 contributes to a significant step height H1 between the pole tip region R1 of the partially etched patterned upper magnetic pole layer 16' and the coil region R2 of the partially etched patterned upper magnetic pole layer 16'. Significant step heights within magnetic pole layers such as the partially etched patterned upper magnetic pole layer 16' are undesirable within the art of inductive magnetic read-write head fabrication since it is often difficult to accurately and reproducibly form upon those magnetic pole layers subsequent layers within the inductive magnetic read-write heads within which are formed those magnetic pole layers.
Various additional features of magnetic pole layer fabrication for use within inductive magnetic write heads have been disclosed by Krounbi et at. in U.S. Pat. No. 5,438,747, the teachings of which are incorporated herein fully by reference.
It is thus desirable to form within magnetic transducer structures which may be employed within inductive magnetic write heads self-aligned partially etched lower magnetic pole layers of permalloy alloy magnetic materials separated by patterned gap filling dielectric layers of aluminum oxide dielectric materials from partially etched patterned upper magnetic pole layers of permalloy alloy magnetic materials with minimal consumption of the partially etched patterned upper magnetic pole layers. It is also desirable to form within magnetic transducer structures which may be employed within inductive magnetic read-write heads partially etched patterned upper magnetic pole layers of enhanced flatness. Most desirable in the art are magnetic transducer structures which simultaneously possess the foregoing two characteristics. It is towards the foregoing goals the present invention is more specifically directed.